Wasabi Posted June 24, 2017 Report Share Posted June 24, 2017 So I have a Briggs and Stratton 148cc lawnmower which has been going strong for over ten years. Last week I noticed it was making a strange noise and was taking longer to start. Today I got it out and it started but only revved at very low revs for about a minute before cutting out. I checked the fuel filter, carb jet, air filter and spark plug before noticing the head gasket had gone round one of the bolts. I took the head off and replaced the gasket. It still won't start. It fires but then idles at very low revs regardless of throttle position and then cuts out after a minute or so. The oil looks really black and it seems to be blowing out the crank breather pipe. Any ideas? Quote Link to comment Share on other sites More sharing options...
ips Posted June 24, 2017 Report Share Posted June 24, 2017 Have you cleaned the carb ? I had similar with mine two weeks ago, stripped carb job sorted Quote Link to comment Share on other sites More sharing options...
Wasabi Posted June 24, 2017 Author Report Share Posted June 24, 2017 Have you cleaned the carb ? I had similar with mine two weeks ago, stripped carb job sorted Yeah took carb to bits earlier and put a fine wire through the jet. All clear. I'm wondering if the piston rings have had it? Quote Link to comment Share on other sites More sharing options...
GingerCat Posted June 24, 2017 Report Share Posted June 24, 2017 Can you adjust the air intake? Mine died over winter but managed to turn up the idle and she lives to cut another day. Quote Link to comment Share on other sites More sharing options...
figgy Posted June 24, 2017 Report Share Posted June 24, 2017 Doubt it's your piston rings more the fuel air not getting through. Piston rings it will either burn oil on four stroke or fail when hot but not when cold on two smoke. Quote Link to comment Share on other sites More sharing options...
iano Posted June 24, 2017 Report Share Posted June 24, 2017 We had this exact problem with a B&S mower as well. Dirty fuel had gunked up the carb. Got it cleaned and she is roaring again. Quote Link to comment Share on other sites More sharing options...
Wasabi Posted June 24, 2017 Author Report Share Posted June 24, 2017 Can you adjust the air intake? Mine died over winter but managed to turn up the idle and she lives to cut another day.Good shout. I'll have a look tomorrow. Thanks Quote Link to comment Share on other sites More sharing options...
Wasabi Posted June 24, 2017 Author Report Share Posted June 24, 2017 Can you adjust the air intake? Mine died over winter but managed to turn up the idle and she lives to cut another day.Good shout. I'll have a look tomorrow. Thanks Quote Link to comment Share on other sites More sharing options...
chris1961 Posted June 24, 2017 Report Share Posted June 24, 2017 (edited) Try putting carb in a ultra sonic cleaner filled with gunk works great but don't tell the wife I used her jewellery cleaner took me ages to get rid of the smell of the gunk engine cleaner she would kill me if she ever finds out Edited June 24, 2017 by chris1961 Quote Link to comment Share on other sites More sharing options...
team tractor Posted June 24, 2017 Report Share Posted June 24, 2017 Have you wash the crank breather? You say it's blowing out of it? We used to wash them in jizer until they rattled again as they got stuck. Not knowing the mower has it got a breather /hole on the top of the fuel cap? If it's blocked it'll restrict fuel Quote Link to comment Share on other sites More sharing options...
saddler Posted June 24, 2017 Report Share Posted June 24, 2017 Old petrol goes off. Drain it & put fresh in Quote Link to comment Share on other sites More sharing options...
team tractor Posted June 24, 2017 Report Share Posted June 24, 2017 Old petrol goes off. Drain it & put fresh in And only takes a month. It's a pain Quote Link to comment Share on other sites More sharing options...
figgy Posted June 24, 2017 Report Share Posted June 24, 2017 I've had cars sat longer than a few months and they started and ran ok on the fuel that had sat in the tank. Must have been lucky with the amount that it kept ok. All my garden tools are ran on aspen2 so I don't get the fuel problems. Quote Link to comment Share on other sites More sharing options...
fortune Posted June 25, 2017 Report Share Posted June 25, 2017 (edited) It might be possible that you have lost/unhooked the carb/governor control spring that hooks in a small hole in the top of the butterfly spindle to a fixed bracket at the front under the air cleaner. This spring counters the governor and controls the running speed. It is quite often knocked off if the m/c has been rodded under bushes. Check operation by using finger on throttle butterfly shaft to see if it returns to position. This is a common cause of this problem Edited June 25, 2017 by fortune Quote Link to comment Share on other sites More sharing options...
myhvslr Posted June 25, 2017 Report Share Posted June 25, 2017 Diaphragm Quote Link to comment Share on other sites More sharing options...
subsonicnat Posted June 25, 2017 Report Share Posted June 25, 2017 Two Replies above have the answer.. Gauze filter,jets dodgy.. Bought an Ultrasonic cleaner,Fired first time,mate had the same problem with his hedge trimmer. Fires up first pull,worth every penny for the cleaner.. PS.... Check your fuel pipes,slightest bit of air getting in,you can pull till next Christmas.. Quote Link to comment Share on other sites More sharing options...
keg Posted June 25, 2017 Report Share Posted June 25, 2017 Diaphragm This was my problem, wouldn't run or kept stalling. Quote Link to comment Share on other sites More sharing options...
Wasabi Posted June 26, 2017 Author Report Share Posted June 26, 2017 This was my problem, wouldn't run or kept stalling.What is the diaphragm and where do I find it? Quote Link to comment Share on other sites More sharing options...
SpringDon Posted June 26, 2017 Report Share Posted June 26, 2017 What is the diaphragm and where do I find it? If it's a classic engine with the carb screwed direct to the petrol tank then the diaphragm sits under the carb. There are 2 bits, the gasket and the diaphragm; the diaphragm must sit on the tank. Sometimes,it's worth replacing the whole carb. Diaphragm kit is about £6 and carb is about 14 which comes with diaphragm. Quote Link to comment Share on other sites More sharing options...
Wasabi Posted June 26, 2017 Author Report Share Posted June 26, 2017 If it's a classic engine with the carb screwed direct to the petrol tank then the diaphragm sits under the carb. There are 2 bits, the gasket and the diaphragm; the diaphragm must sit on the tank. Sometimes,it's worth replacing the whole carb. Diaphragm kit is about £6 and carb is about 14 which comes with diaphragm. Ah right. The carb is on the side of the engine, below the air intake. Quote Link to comment Share on other sites More sharing options...
SpringDon Posted June 27, 2017 Report Share Posted June 27, 2017 If the carb does not sit on a metal tank then the chances are it has a float (does the carb have a bowl under it) rather than a diaphragm. If this is the case, an sonic cleaner or solvent bath are in order. It moght also be worth checking the compression, less than 80psi might indicate ring problems or valve clearances need checking. But fuel or governer seem most likely. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.